Field of the Invention
The present invention relates to an exposure apparatus, stage apparatus, and device fabrication method.
Description of the Related Art
An exposure apparatus for fabricating a semiconductor device includes a reticle stage for holding and positioning a reticle (mask), and a substrate stage for holding and positioning a substrate. In a step-and-scan exposure apparatus (scanner) which is currently mainstream, the reticle stage and substrate stage repeat acceleration and deceleration to move and stop for each shot region on a substrate.
In such an exposure apparatus, the processing velocity (throughput) is increased by increasing the accelerations of the reticle stage and substrate stage in order to increase: the productivity. As the accelerations of the stages increase, forces acting on a reticle and substrate held by the stages increase. In particular, the reticle stage moves at an acceleration higher than that of the substrate stage and thus requires a force (holding force) for holding a reticle against the acceleration. Recently, clamp holding of holding a reticle or substrate from its upper surface by a clamp is employed to enhance the holding force, in addition to conventional vacuum chuck.
There are various types of reticles and substrates held by the stages. For example, reticles include a general reticle (reticle obtained by drawing a circuit pattern on a glass substrate) used to fabricate a semiconductor device, and a special reticle used for a special purpose, for example, for a tool or measurement. Such special reticles include reticles of different shapes, materials, and masses, such as a reticle on which optical elements are arrayed on the upper or lower surface, and a reticle made of a metal. For the reticle on which optical elements are arrayed, the above-mentioned clamp holding cannot be adopted because the optical elements may be damaged. In some cases, the frequency characteristic changes depending on the difference in the material and mass of a reticle, and the stage may oscillate.
As a technique for suppressing oscillation of the stage caused by a change of the frequency characteristic, Japanese Patent Laid-Open No. 2010-198315 has proposed a method of changing the control parameters of a stage in accordance with the mass of a load mounted on an X-axis driving unit. In Japanese Patent Laid-Open No. 2010-198315, oscillation of the stage can be suppressed by setting optimal parameters for the stage in accordance with a change of the frequency characteristic.
However, the eigenvalue changes depending on the material of a reticle or substrate held by the stage. Thus, the resonance frequency of the stage may change to oscillate the stage. In this manner, the resonance frequency does not change depending on only the mass. Therefore, even if the control parameters are changed in accordance with the mass, as in the technique in Japanese Patent Laid-Open No. 2010-198315, oscillation of the stage cannot he completely suppressed. When the reticle can neither be clamped nor held, and the stage is moved at a high acceleration, this may cause: a positional shift of the reticle or damage to the reticle.